Bidirectional Protocol Independent Multicast (Bidir PIM) is a member of the suite of multicast routing protocols which also includes dense-mode, sparse-mode, and source specific multicast (SSM). Bidir PIM was developed to help deploy emerging communication and financial applications that rely on a many-to-many applications model. Bidir PIM allows these applications to easily scale to a very large number of groups and sources by eliminating the maintenance of source states.
Traditional PIM protocols (dense-mode and sparse-mode) provided two models for forwarding multicast packets: source trees, and shared trees. Source trees are rooted at the source of the traffic while shared trees are rooted at the rendezvous point. Each model has its own set of characteristics and can be optimized for different types of applications. The source tree model provides optimum routing in the network, while shared trees provide a more scalable solution. Source trees achieve the optimum path between each receiver (or recipient) and the source at the expense of additional routing information such as a routing entry per source in the multicast routing table. This is acceptable in applications with a limited number of sources. Applications like live broadcasts and distance learning are some examples where only one or a few sources are active. On the other hand, the shared tree provides a single distribution tree for all of the active sources. This means that traffic from different sources traverse the same distribution tree to reach the interested receivers, thereby reducing the amount of routing states in the network. Bidir PIM (a variant of PIM sparse-mode) uses these shared trees as its main forwarding mechanism.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.